Hoisting device, with compensator built into hoisting cable system

ABSTRACT

The invention is a hoisting device for a vessel with a mast in the form of a tube or sleeve with fixed cable blocks on the top side, a trolley with moveable pulleys, a feature on the bottom side for gripping a load, a hoisting system with at least a hoisting cable and a winch, wherein the hoisting cable is guided over the cable blocks and pulleys of both the mast and the trolley in order to move the trolley relative to the mast with the aid of the hoisting system, and a compensator located in the mast in the form of a pneumatic or hydraulic cylinder for damping movements of the vessel as a result of heave and beating of the waves characterized in that the hoisting cable is guided over cable pulleys that are connected to the ends of the compensator.

FIELD OF THE INVENTION

The present invention relates to a hoisting device, provided with amast, on the top side provided with cable blocks; a trolley, which ismovably fixed on the mast, on the top side is provided with cableblocks; and on the bottom side is provided with means for gripping aload; hoisting means, at least equipped with a hoisting cable and awinch, said hoisting cable being guided over the cable blocks of boththe mast and the trolley, and it being possible to move the trolleyrelative the mast with the aid of the hoisting means; and a compensator,in the form of a pneumatic or hydraulic cylinder, for damping movementsof the vessel as a result of heave and beating of the waves.

BACKGROUND OF THE INVENTION

Various hoisting devices are known from the prior art. These hoistingdevices are used in the offshore industry as drilling masts on, forexample, drilling vessels. When, in use, a drill string is attached tothe bottom side of a trolley, also known as a traveling block, thecompensator has to compensate for the movements of the vessel relativeto the seabed. The drill string itself will rest at least partially inthe earth's surface during the drilling and will make a minimal movementrelative to the earth's surface. The vessel, on the other hand, doesmove under the influence of the waves and the flow of the water.

According to the prior art, the compensator is generally placed betweentwo blocks or trolleys, both of which can move relative to the mast. Inthis case the top trolley will be provided with cable pulleys, which canbe moved relative to the mast with the aid of a hoisting cable. Thebottom trolley will be attached to the top trolley by means of thecompensator. When in this construction forces are exerted by the drillstring upon the bottom trolley, these forces will be transmitted onlypartially to the top trolley.

The compensator generally used operates hydro-pneumatically. Thehydro-pneumatic compensator will therefore be connected to a compressedair device by means of hoses, pipes and the like. A relatively largestroke volume is necessary for good functioning of such a compensator.Since both blocks or trolleys move relative to the mast, the compensatorwill also be able to move relative to the mast, which is a disadvantage.The connections of the compressed air device to the compensator must infact also be able to move relative to the mast. This requires the useof, for example, flexible hoses and pipes, and all that makes theconnection relatively complex, and therefore expensive.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide for a hoistingdevice according to the type mentioned in the preamble, in which theconnections of a compressed air device to the compensator can be fittedat a stationary point.

That object is achieved in the present invention by the fact that thehoisting cable is guided over cable pulleys which are connected to theend of the compensator, all the above in such a way that force can beexerted upon the hoisting cable with the aid of the compensator.

That means that the compensator is no longer placed between the trolleyswhich are attached to the mast, but that the compensator acts directlyupon the hoisting cable. The compensator can be connected by a first endto a stationary section of the mast. At the other end, the compensatoris connected to the hoisting cable by way of cable pulleys. Tension canthus also be applied to the hoisting cable by means of the compensator.

The advantage of these measures is in the first place that thecompensator can be fastened in a fixed position in the vicinity of themast. The connection of the compressed air device to the compensator cantherefore be made a t one point. That makes a relatively simple andcheap construction possible.

The hoisting device according to the invention can be improved furtherby the device comprising at least two compensators, each of which isconnected to cable pulleys at its end.

The effect of this measure is that the device acquires greaterredundancy. If the compensator in a device according to the prior artbreaks down, the drilling operations must be stopped immediately With ahoisting device according to the invention, containing more than onecompensator, it is possible to continue working should one of thecompensators break down. The cylinder of the compensator which fails islocked in that case. Locking the compensator will mean that the strokeof the bottom trolley is reduced, but because one or more compensatorsthat are still active remain, the device does not have to be shut down.

It is advantageous according to the invention for the mast to bedesigned in the form of a tube or sleeve, and for the compensator(s) tobe place in the mast.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described further with reference to theappended drawings, in which:

FIG. 1 shows the hoisting device according to the present invention;

FIG. 2 shows a diagrammatic view of the fastening of the rods asdescribed on page 10, lines 26-34;

FIG. 3 shows a diagrammatic view of the operation of the riser connectwinch via the compensator to the riser;

FIG. 4 shows the case where four loose pulleys are attached to thetrolley;

FIG. 5 shows the case where two loose pulleys are attached to thetrolley and two loose pulleys are attached to the mast head;

FIG. 6 shows the case where four loose pulleys are attached to the masthead;

FIG. 7A-7B shows a front view of a possible embodiment of the loosepulleys;

FIG. 8 shows a side view of one of the loose pulleys according to FIG.7A;

FIG. 9 shows a second embodiment of loose pulley;

FIG. 10 shows diagrammatically the run of the hoisting cable over thevarious pulleys, in the case where four loose pulleys are attached tothe trolley;

FIG. 11 shows diagrammatically a second possibility for reeving thehoisting cable;

FIGS. 12a, 12 b and 12 c show the relationship between the number ofparts of hoisting cable between the mast head and the trolley, on theone hand, and the number of parts of connecting cable between the masthead and solid ground, on the other hand;

FIGS. 13a-13 e show stepwise the transition form a situation in which oncompensation occurs to a situation in which full compensation occurswith the aid of the connecting cable;

FIGS. 14a-14 d show stepwise the transition from a situation with fullcompensation using the connecting cable to a situation withoutcompensation;

FIGS. 15-16 show diagrammatically the possibility of placing objects onthe ground beneath the vessel using the hoisting device with passivecompensation according to the present invention, fixed on a vessel.

DETAILED DESCRIPTION

There is generally sufficient space in the mast on a drilling vessel ora comparable vessel for placing the compensator. That means that thecompensator itself will not require any additional space. In addition tothe advantage of the space gain achieved, it is important that the mastremains readily accessible from all sides through the placing of thecompensator in the mast. The compensator thus does not constitute anyobstacle to, for example, the supply of equipment to the mast.

In the devices according to the prior art it is customary for a hoistingcable to be attached to a fixed point at one end. The other end of thehoisting cable is then wound around a winch. If this winch breaks down,it is no longer possible to work with the device.

It is therefore advantageous for the hoisting means to be provided withtwo winches, each end of the hoisting cable being wound onto a separatewinch. By now winding the two ends onto a separate winch, it is possibleto achieve the same cable speed at a relatively low speed of revolutionof the winches. That means an enormous reduction in the wear on thecable, with the result that the cable does not have to be replaced asoften.

Moreover, by adding the second winch, redundancy is provided in thesystem. Should one of the winches fail, then the hoisting device is notunusable, but it is possible to continue working with a single winch. Itis advantageous for the winches to be driven by a plurality ofrelatively small motors.

For example, it is possible to equip the winches on both sides withelectric motors which engage with a pinion in a toothed wheel of thewinch. First, this has the advantage that such electric motors arecommercially available. For the use of the hoisting device it istherefore not necessary to develop a special, and therefore expensive,hoisting winch. Secondly, the relatively small motors have a lowinternal inertia, which means, for example, that when the direction ofrotation of the winch is reversed less energy and time are lost duringthe reversal.

In the case of a hoisting device according to the prior art of the typementioned in the preamble, finding the optimum compromise between speedand power is a known problem. The hoisting cable is guided in such a wayover the cable blocks in the mast and on the trolley that several cableparts extend between the mast and the trolley. In this case the morewire parts are present between the mast and the trolley, the greaterwill be the load that can be lifted with the hoisting device if thehoisting winch remains unchanged. However, in this case the more wireparts are present between the mast and the trolley, the lower will bethe speed at which the trolley can be moved relative to the mast.

In order to find a good compromise between speed and lifting power, itis generally decided to provide the hoisting device with relativelyheavy winches. The heavy winches ensure that the requirement of beingable to move the trolley up and down rapidly can be met in every case.However, that also means that a substantial part of the lifting power isnot being utilized for a substantial part o f the time. In other words,the device is actually provided with too heavy—and therefore tooexpensive—winches to be able to reach sufficient speed occasionally.

It is therefore a further object of the present invention to provide ahoisting device of the type mentioned in the preamble. By means ofwhich, on the one had, a relatively heavy load can be lifted and on theother hand, which can be operated at a relatively high speed, while thehoisting means can be of a relatively light and cheap design.

The object is achieved in the present invention by the fact that thehoisting cable is also guided over loose pulleys, which can be movedbetween a first position, in which the loose pulleys are connected tothe mast, and a second position, in which the loose pulleys areconnected to the trolley.

The effect of this measure is that the number of wire parts between themast and the trolley can be set as desired. When the loose pulleys areattached to the mast, few wire parts will extend between the mast andthe trolley, and a relatively low weight can be lifted. When the looseblocks are attached to the trolley, a relatively large number of wireparts will extend between the mast and the trolley, and the trolley canbe moved a t a relatively low speed relative to the mast. Since thehoisting cable is guided over the pulleys and the pulleys can beattached as desired to the mast or to the trolley, the hoisting cabledoes not have to be reeved again. That means that the desired number ofwire parts can be set in a relatively short time.

It is possible according to the invention for the loose pulleys to beattached symmetrically relative to the center of the mast.

This ensures that the forces exerted upon the cables are alsotransmitted symmetrically to a mast, which means that no additionalbending loads are exerted upon the mast.

It is possible according to the invention for the loose pulleys to beaccommodated in a housing, which at least on the bottom side is providedwith locking elements for fixing the pulleys on the trolley. The loosepulleys are pulled automatically into their first position, in contactwith the mast, by tension in the hoisting cable. It is thereforesufficient to provide the bottom side of the pulleys with lockingelements.

It is advantageous for the locking elements to be equipped with ahydraulic actuation device. The use of a hydraulic actuation devicemeans that the locking pins can be remotely controlled.

The hoisting device according to the invention is further improved bythe fact that the hoisting device is provided with a connecting cable,for connecting the vessel to a stationary section, such as the top sideof the riser, which connecting cable is guided over the cable pulleysconnected to the end of the compensator, in order to be able to exert aforce upon the compensator with the connecting cable.

The term ‘stationary section’ according to this description is intendedto convey a section which forms part of or is connected to the seabed.

The connecting cable will be fitted in such a way that when the vesselmoves upwards relative to the seabed, additional force is applied to thecompensator, so that its length increases. The pulleys connected to thecompensator consequently move to the topside of the mast, so that a loadconnected to the hoisting cable will move downwards. When the vesselmoves downwards, the opposite occurs. Since the connecting cable isconnected to a stationary section, the load itself will not moverelative to the seabed. The heave can be compensated for entirely withthe aid of the connecting cable. It is obvious to connect the connectingcable to the topside of the riser. In that case the connecting cablecould also e called a “riser connect winch.

It is further possible for each end of the connecting cable to be woundonto a separate winch”.

It is further advantageous to provide one of the winches with a slipbrake, for paying out the connecting cable when a maximum pulling forcein the connecting cable is exceeded. The slip brake ensures that amaximum pulling force can be applied to the connecting cable if that isdesired in use. If the force on the cable becomes higher, the winch willpay out the cable so that the pulling force does not exceed thepreviously set value.

It is further advantageous for the connecting cable also to be guidedover loose pulleys, which are movable between a first position, in whichthe loose pulleys are connected to the mast, and a second position, inwhich the loose pulleys are connected to the stationary section, such asthe top side of the riser.

For good functioning of the heave neutralization by means of theconnecting cable, the working length of the connecting cable must beadapted to the working length of the hoisting cable. That means that themoment the number of parts of the hoisting cable between the mast andthe trolley is changed, it must also be possible to change the number ofparts of the connecting cable between solid ground (riser) and the mast.

According to the invention, it is further possible for the mast to beprovided at the topside, on both sides of the hoisting cable, with afastening for attaching a pull rod or pull cable. These fastenings caneach be used for coupling a pull rod, for example a drill pipe, whichpull rods are connected by means of a clamp at the bottom side. Saidclamp can be used for clamping, for example, the drill string. Thisproduces in a simple and advantageous manner a system that ensures thata load can be attached to the mast, while the hoisting block above theload is free for carrying out hoisting operations.

The present invention in a second aspect relates to a method, by meansof a passive compensator, for placing an object on the ground.

The method according to the present invention is characterized in that:the compensator is placed under a tension that is equal to theunderwater weight of the object that has to be taken downwards by thehoisting device,

the object is moved downwards by paying out the hoisting cable with theaid of the winch,

the hoisting cable continues to be paid out until the object makescontact with the bottom. At that moment a switch-over is made to the lowgas pressure system,

the object now remains standing on the seabed at a previously set gaspressure.

In the manner described above it is possible for a heavy object to beplace in a very controlled manner on the ground beneath a vessel. Thedanger of an object hitting the ground with great force and consequentlybeing damaged is minimized in this way.

FIG. 1 shows the hoisting device 1 according to the present invention.The hoisting device 1 comprises a mast 2. In the description below theterm mast will always be used, but it must be understood that any othersuitable device, such as, for example, a tower, could also be used.

The topside of the mast 2 is formed by a masthead 3. A large number ofcable pulleys are fixed in the masthead 3. First, two cable pulleys 4are fitted on an axis 41. Below that, on the rear side of the mast, fourcable p pulleys 5 are mounted on an axis 51. On the front side of themast, four cable pulleys 6 are mounted on an axis 61. Furthermore, amiddle pulley 7 is fixed on the front side of the mast, the axis of saidpulley 7 being substantially perpendicular to the axis of the pulleys 4,5, and 6.

The hoisting device further comprises a trolley 10. Said trolley 10 canmove along a guide 11 relative to the mast 2. On the bottom side, thetrolley 10 is provided with a bracket or hook 12, or some other suitablemeans, to which a load to be hoisted can be attached. FIG. 1 shows thecase in which a top drive 13 with a drill string 14 fixed below it isattached to the hook 12. On the top side, the trolley 10 is providedwith two cable pulleys 15. The trolley 10 is connected to the mast head3 by the cable 16, which runs by way of several reevings between thecable pulleys 15 on the trolley and the various cable pulleys in themast head 3.

In addition to the above mentioned cable pulleys 4, 5, 6, 7 and 15, four“loose pulleys” 17 are also present in the hoisting device 1. Theseloose pulleys 17 may be attached as desired to the mast head 3 or to thetrolley 10. The coupling of the loose pulleys 17 to the mast head 3 orto the trolley 10 is shown in detail in FIGS. 4-9.

The advantage of the presence of the loose pulleys 17 is that the numberof wire parts of the cable 16 that extend between the mast head 3 andthe trolley 10 can be varied. If the loose pulleys 17 are attached tothe mast head 3, a limited number of wire parts will extend in thedirection of the trolley 10. That means that, on the one hand, arelatively limited weight can be lifted with he aid of the hoistingdevice, but, on the other hand, the trolley 10 can be moved relativelyquickly in the direction of the mast head 3. If the loose pulleys 17 areattached to the trolley 10, a relatively large number of wire parts willextend from the mast head 3 in the direction of the trolley 10. Thatmeans that a relatively great weight can be lifted with the aid of thetrolley 10, but that said trolley 10 will be moved at a relatively slowspeed relative to the mast head 3. By distributing the number of loosepulleys 17 as desired over the mast head 3 and the trolley 10, it isensured that both the weight to be lifted with the hoisting device andthe speed at which the trolley 10 can be moved relative to the mast head3 are adjustable.

In the prior art a known problem is that a hoisting device often has tobe equipped with a relatively large drive, in order to be able toachieve a workable compromise between the maximum lifting power and theminimum speed to be achieved. This problem is solved by the “loosepulleys” according to the present invention.

In the hoisting device 1 according to FIG. 1 the cable 16 extends from afirst hoisting winch 18 in the direction of the mast head 3. Thehoisting winch is also known as a draw work. The hoisting cable 16 issubsequently guided back to a second hoisting winch 19. In the prior artit is customary for an end section of the hoisting cable 16 to be fixedat a fixed point, the other end being rolled up on a hoisting winch.Several advantages can be obtained by making use of two hoisting winches18, 19, as in the hoisting device 1. In order to achieve a certain speedof the trolley relative to the mast head 3, the speed of rotation of thehoisting winches 18 and 19 can be kept twice as low as it could if onlyone hoisting winch were used. The effete that can be obtained by keepingthe speed of the hoisting winches 18, 19 relatively low is that littlewear will occur in the cable 16. Should one of the two hoisting winchesfail during use, work can continue using another hoisting winch. In theprior art the failure of a hoisting winch immediately means that thehoisting device can no longer be used. The hoisting winches 18, 19 arepreferably driven by electric motors. In the case of each hoistingwinch, for example, each side of the hoisting winch 18, 19 can beprovided with such a motor. That means that each hoisting winch isdriven by 2 electric motors. First, this has the advantage that theelectric motors to be used can be kept relatively small, which meansthat these motors do not have to be designed specifically for thehoisting purposes, but will be in stock on the market. Secondly, the useof the relatively small motors has the effect that the internal inertiain the motors is kept low. That means that when the direction ofrotation of the winches 18, 19 is reversed the internal inertia of thedrive elements themselves will not give rise to problems.

In FIG. 1, in addition to the cable pulleys mentioned, there is furthera first set of two and a second set of two cable pulleys 20, connectedto the top side of two compensators 21, The compensators 21 areconnected at the bottom side in the connection point 22 to the mast 2.The hoisting device 1 according to the present invention canadvantageously be used for numerous hoisting operations. The hoistingdevice 1 is particularly advantageous when used in the case of drillingoperations, from a vessel. The reason for this is that, particularly inthe case of such drilling operations, in some parts of the drillingprocesses has to be possible for a very great hoisting force to beapplied, and that in other parts of the drilling process the speed atwhich the trolley can move relative to the mast in the most importantfactor. In the case of hoisting devices which are used on such drillingvessels, it is common to place a compensator in the device. Saidcompensator is generally fitted on the bottom side of the trolley 10. Adevice is then place on the bottom side of the compensator, to whichdevice, for example, the top drive of a drill string can be connected.By means of such a fastening of the compensator, the compensator willmove relative to the mast. For good functioning, the compensator must beconnected to supply means for compressed air. When the compensator movesrelative to a mast, this compressed air installation must be connectedin a complex—and therefore relatively expensive—manner to thecompensator, for example by means of flexible hoses and the like.

According to the invention, it has now been decided to fit thecompensators 21 in the mast 2, in which case the bottom side 22 of thecompensators will be attached to a stationary point of the mast 2. Theposition of the bottom side of the compensators relative to the mast istherefore the same at all times. That means that the installation forsupplying air pressure can always be connected to the compensators 21 atthe same point. This ensures that the coupling between the air pressureinstallation and t h e compensators can be made many times simpler thatis the case in the prior art.

Two compensators 21 are deliberately illustrated in the mast. The device1 can function extremely well with only one compensator 21, but theaddition of at least a second compensator is advantageous. Should one ofthe two compensators fail to function or break down, it is stillpossible to go on working with the aid of the device. In the prior artthe breakdown of the compensator meant immediate stoppage of thehoisting device. That is prevented with the invention.

The hoisting device according to FIG. 1 is further provided with aconnecting cable, which provides for a connection between solid groundand the pulleys 20 which are connected to the compensators 21. Theconnecting cable is omitted in FIG. 1 in order to keep the drawing clearto view. The functioning of the connecting cable is explained withreference to FIG. 3.

The mast according to FIG. 1 is illustrated diagrammatically in FIG. 2.The mast 2 is provided with fastenings 101 on the top side. Thesefastenings 101 can each be used for connecting a pull rod, for example alength of drill pipe 102, which pull rods are connected at the bottomside by means of a clamp 103. Said clamp 103 can be used for clamping,for example, the drill string 14, at a moment when the drill string doesnot need to move up and down with the aid of the trolley 10. This is asimple and advantageous way of producing a system which ensures that aload can be attached to the mast 2, while the hoisting block 10 abovethe load is free for carrying out hoisting operations.

FIG. 3 shows a diagrammatic side view of the drill mast according toFIGS. 1 and 2. In addition to the hoisting cable 16, the connectingcable 105 can also be seen. This connecting cable 105 is guided over thecable pulleys 20, which are connected to the end of the compensator 21.The object of this is to be able to exert a force on the compensator 21with the connecting cable 105. The presence of the connecting cable 105means that there is a connection between the pulleys 20 and the seabed,or a section that is connected to the seabed.

The connecting cable 105 will be fitted in such a way that when thevessel moves upwards relative to the seabed, additional force is exertedupon the compensator 21. This makes the compensator 21 longer. Thepulleys 20 connected to the compensator 21 move in the direction of themast head 3. This releases a section of the hoisting cable that wasclamped in the mast 2 between the top side of the mast and the pulleys20, so that a load connected to the hoisting cable 16 moves downwards.When the vessel moves in the direction of the seabed, the oppositeoccurs. Since the connecting cable 105 is connected to a stationarysection, the load itself will not move relative to the seabed. The heavecan be compensated for completely with the aid of the connecting cable.

It is also possible foe each end of the connecting cable 105 to be woundonto a separate winch 106, 107. In use, it is advantageous if theconnecting cable can either be hauled in/paid out very quickly or thehauling in of the cable can be carried out with great force. The placingof the connecting cable 105 in position and the operation of the winches106 and 107 are explained with reference to FIGS. 13a-13 e.

The possibility of varying the number of hoisting parts between the masthead 3 and the trolley 10 is built into the system of the hoisting cable16. This possibility is discussed in detail with reference to FIGS. 4-9.For good functioning of the heave neutralization by means of theconnecting cable 105, the working length of the connecting cable 105must be adapted to the working length of the hoisting cable 16. In otherwords, the moment the number of parts of the hoisting cable 16 betweenthe mast 2 and the trolley 10 is changed, it must also be possible tochange the number of parts of the connecting cable 105 between solidground (riser) 78 and the mast 2.

FIG. 4 illustrates the case where four loose pulleys 17 are attached tothe trolley 10. It can be seen in FIG. 4 that four pulleys 17 areattached to the trolley 10. This means that twelve wire parts extendbetween the trolley 10 and the mast head 3.

FIG. 5 shows the case where two loose pulleys 17 are attached to themast head 3 and two loose pulleys 17 are attached to the trolley 10. Inthis case eight wire parts will extend between the mast head 3 and thetrolley 10.

FIG. 6 shows the case where four loose pulleys 17 are attached to themast head 3. That means that only 4 wire parts will extend between themast head 3 and the trolley 10. As will be understood, the highestweight can be lifted in the configuration according to FIG. 4, since inthat case twelve wire parts extend between the mast head 3 and thetrolley 10. In the configuration according to FIG. 6 relatively littleweight can be lifted since only four wire parts extend between the masthead 3 and the trolley 10. However, the trolley 10 can be moved at arelatively high speed relative to the mast head 3.

It can be seen in FIGS. 4, 5 and 6 that on the left-hand side of themast 2 exactly the same number of loose pulleys 17 are attached to themast head 3 as on the right-hand side. That means that the forces of thecable 16 on the mast will be distributed symmetrically.

FIG. 7A shows a front view of a part of the trolley 10, with a fixedpulley 15 and loose pulleys 17 thereon. The block will be designedsymmetrically, with loose pulleys 17 being placed on both sides of thefixed pulley (only two pulleys 17 are illustrated in the figure). On thebottom side, the loose pulleys 17 are provide with a lock or hook 104which interacts with a lug or pin 121 on the trolley 10. The pulleys 17can be fixed on the trolley as desired. Since there will always be acertain tension on the hoisting cable 16, the loose pulleys 17 arepulled automatically in the direction of the mast head 3. For thatreason, fastening means can be dispensed with on the top side of thepulleys 17. However, if the tension is lost completely, a pulley 17 willfall downwards by the force of gravity. In order to be on the safe side,the hoisting device is therefore provided with a safety facility, whichcan be as designed in, for example, FIG. 7B. According to FIG. 7B, apulley 17 is provided on its top side with two balls which are connectedto the housing of the pulley 17 in such a way that they are movablerelative to each other. The balls are accommodated in recesses 123 inthe mast head 3. If no force at all is exerted upon the pulley 17, theforce with which the balls lock the pulley in the mast head issufficient to hold the pulley 17 in place. However, if a slight force isexerted upon the pulley, the balls are released from the recesses, andthe pulley 17 can the move downwards.

FIG. 8 shows a side view of one of the loose pulleys 17 according toFIG. 7A. The lock 104 is shown in two positions. The position of thelock is determined with the aid of a cylinder 124. When the cylinder isnot actuated, the lock falls behind the pin 121 during to-blocks pulling(see above). The pulley 17 is thus connected to the trolley 10. When thetrolley 10 during use is move relative to the mast head 3, the trolley10 takes that loose pulley 17 along with it downwards. If, on the otherhand, the cylinder is actuated, the hook cannot grip behind the pin1221, and that means that the trolley 10 cannot take the pulley alongwith it, so that the pulley 17 remains behind in the mast head 3.

The cylinder 124 by means of which the lock 104 is operated has beendeliberately placed in the mast head 3. The fact is that the trolley 10goes into the so-called Hazardous Area on a drilling platform or vessel.During the drilling, gas or oil can escape in this area. Non-explosiveequipment must be worked with in the Hazardous Area. For that reason, ithas advantages to place the cylinder 124 on /in the mat head 3.

FIG. 9 shows a further embodiment of the loose pulley 17, the loosepulley 17 comprises an outer housing consisting of two plates 53. Bothon the top side and on the bottom side, these plates 53 are providedwith eyes 54, in which locking pins are received. Said locking pins movethrough eyes 55, which are cut out in, for example, a U-shaped fasteningelement 51. This fastening element 51 can be attached either to thetrolley or to a mast head. In use, the trolley 10 will be hoisted to aposition as close as possible to the mast head 3. This position is alsoknown as to-blocks. After that, either the locking pins 52 belonging tothe trolley 10 or the locking pins 52 belonging to the mast head 3 willbe moved into the eyes 54 of the plates 53. In this way a choice can bemade concerning which loose pulleys 17 are connected to the mast head 3and which pulleys 17 are connected to the trolley 10.

FIG. 10 shows the run of the cable 16 from the hoisting winch 18 overthe successive cable pulleys in the direction of the hoisting winch 19.FIG. 10 shows the case where the four loose pulleys 17 lie substantiallyin line with the two pulleys 15 which are immovably fixed to thetrolley. That means that in the case shown in FIG. 10 twelve wire partswill extend between the mast head 3 and the trolley 10.

FIG. 11 shows a further reeving plan for the hoisting cable 16 which canbe used for the device according to the invention.

In FIGS. 12a-12 c the setting of the correct number of hoisting parts inthe hoisting cable 16 and the connecting cable 105 respectively isillustrated further. It can be seen in the figures that the connectingcable is guided over at least one loose pulley 125. Said loose pulley125 is movable between a position in contact with the mast head 3 (seeFIG. 12b) and a position in which the loose pulley 125 is situated inthe vicinity two further pulleys 127, which guide a further part of theconnecting cable (FIGS. 12a and 12 b).

According to FIG. 12a, there are twelve hoisting parts in use betweenthe mast head 3 and the trolley 10. This large number of hoisting partsin the hoisting cable 16 is generally used only during the placing ofthe riser and the BOP (see FIGS. 15-18). In that case the riser connectwinch is not needed. It can therefore be seen in FIG. 12a that theconnecting cable 105 is not being used in this case.

According to FIG. 12b, there are eight hoisting parts in use between themast 2 and the trolley 10. In this case the loose pulley 125 over whichthe connecting cable 105 is being guided is in contact with the masthead 3. Between said mast head 3 and the fastening of the connectingcable 105 to solid ground (riser 78) there are four parts in use.

According to FIG. 12c there are only four hoisting parts present betweenthe mast head 3 and the trolley 10. In this case the loose pulley 125 isconnected to the remaining pulleys 127.

FIGS. 13a-13 e show stepwise the transition from a situation in which nocompensation occurs (no connecting cable active) to a situation in whichfull compensation occurs with aid of the connecting cable. Inparticular, FIGS. 13a-13 e shows the compensator (21), the connectingcable (105), winches (106 and 107), and the hoisting cable (16).

Putting the riser connect winch into position is carried out as follows:

The compensator 21 is positioned in the lowest position the moment thevessel finds itself in the trough of a wave or moves downwards (FIG.13a). A certain pulling force is then exerted upon the connecting cable105. At least one of the winches 106, 107 (shown in FIG. 10) is operatedin such a way that the connecting cable 105 can follow the movement ofthe vessel relative to the seabed (FIG. 13b). The winches 106 and 107are controlled in such a way that they take the slack out of heconnecting cable. When the cable is taut, the passive compensator istaken slowly to the middle position. The riser connect winches are thenstopped and there is active compensation in the system by means of theconnection of the riser.

The connecting cable can also be used during drilling. The moment adrill head on a drill string makes contact with the earth's surface thetension on the hoisting cable 16 will decrease slightly. This decreasein the load upon the hoisting cable is taken over by the connectingcable. Depending on the rigidity of the drill string and the hardness ofthe ground, this load will vary between a value equal to zero and thevalue of the full weight of the drill string. On account of the possiblyhigh loading on the connecting cable 105, care must be taken to preventoverloading of said cable 105 (13 e).

FIGS. 14a-14 d show stepwise the transition from a situation with fullcompensation (using the connecting cable) to a situation withoutcompensation. In particular, FIGS. 14a-14 d shows the compensator (21),the connecting cable (105), winches (106 and 107), and the hoistingcable (16).

When the function of the connecting cable has to be ended, first of alla maximum tension is placed upon the connecting cable 105 by means ofthe fast winch (14 a).

The cable on the winch is hen paid out, and the compensator slidesin/out.

If desired, the compensator can be locked if it is slid in fully. Inaddition, the cable on the winch is paid out further, so that theconnecting cable ultimately hangs loose.

A known problem in the case of drilling vessels according to the priorart is the placing of heavy objects on the bottom of, for example, thesea. With reference to FIG. 12a, it is pointed out above that theconnecting cable 105 is not used during the placing of objects, such asthe riser and the BOP, on the seabed. Owing to the presence of thepassive compensators in the reeving of the hoisting cable 16, theplacing of such objects on the seabed according to the invention can,however, be carried out in an advantageous manner. This is describedbelow with reference to FIGS. 15 and 16.

According to FIGS. 15 and 16, a load, such as, for example, a blow-outpreventer (BOP) 71 is moved in the direction of the seabed 900 beneath adrilling vessel 70 (shown diagrammatically). The BOP is, for example,placed on a template 72 present on the seabed 900. Since the drillingvessel 70 will never be entirely stationary relative to the seabed 900,owing to the waves and the heave, during the placing of the BOP 71 onthe template there is the risk that, owing to the heave of the vessel70, the BOP will be placed on the template 72 at an uncontrolled speed.The BOP 71 could be damaged as a result. According to FIG. 16, the loadhas reached the seabed 900.

The system according to FIGS. 15 and 16 works as follows:

The installation on the vessel 70 consists of one or two hydrauliccylinders or compensators 12. Said compensators 21 are connected topressure vessels 130 filled with gas, so that a certain pre-pressure isbuilt up in the pressure vessels. The compensators 12 are connected tothe pressure vessels 130 by way of a medium separator 131, also known asa hydraulic accumulator. The pre-pressure or P(load) of one of thepressure vessels corresponds to the hydraulic pressure in thecompensator that is needed to keep the load 71 in balance under water.Another pressure vessel 130 is provided with a low pre-pressure P(low)which corresponds to the tension on the hoisting cable 16 at the momentwhen the load 71 makes contact with the seabed (see FIG. 16). Variousvalves 132 are incorporated in the system, in the connection between thehydraulic compensator 21, the hydraulic accumulator 131 and the pressurevessels 130.

When the load is under water, the loading in the hydraulic compensators21 corresponds to the loading upon the hoisting device. The hydrauliccompensators are connected to only one of the pressure vessels 130, byway of the hydraulic accumulator 131. During the sinking of the load,the valves A and C (see FIGS. 15 and 16) are open, while the valves Band D are closed The system reacts as a heave compensator with a rigidcharacteristic. The operator of the system can determine the position ofthe load by means of the hoisting device. When the load 71 reaches theseabed, the valves A and C are closed and the valves B and D are openedsimultaneously. At that moment the system reacts as a system of constanttension, in the case of which the loading upon the hoisting device iskept constant at a predetermined (low) value. Since a relatively largegas volume is present in the hydraulic accumulators, the system now hasthe characteristic of a slack spring. In this configuration the systemcompensates for movements of the vessel 70 relative to the seabed.

What is claimed is:
 1. A hoisting device (1) for a vessel comprising: amast (2) on the top side provided with fixed cable blocks; a trolley(10) including pulleys, which are moveable, and on the bottom side isprovided with means (12) for gripping a load; hoisting means, at leastequipped with a hoisting cable (16) and a winch (18), the hoisting cable(16) being guided over the cable blocks and pulleys of both the mast andthe trolley, to move the trolley (10) relative to the mast (2) with theaid of the hoisting means; and at least two compensators in the form ofpneumatic or hydraulic cylinders, for damping movements of the vessel(70) as a result of heave and beating of the waves, characterized inthat the hoisting cable (16) is guided over cable pulleys (20) which areconnected to the ends of the compensators, the mast is designed in theform of a tube or sleeve, and in that the compensator (21) is placed inthe mast (2) and each of said compensators are connected to cablepulleys (20) at its end.
 2. A hoisting device (1) for a vesselcomprising a mast (2) on the top side provided with fixed cable blocks;a trolley (10) including pulleys which are moveable, and on the bottomside is provided with means (12) for gripping a load; hoisting means, atleast equipped with a hoisting cable (16) and a winch (18,19), thehoisting cable (16) being guided over the cable blocks and pulleys ofboth the mast and the trolley, to move the trolley (10) relative to themast (2) with the aid of the hoisting means; and a compensator (21) inthe form of a pneumatic or hydraulic cylinder, for damping movements ofthe vessel (70) as a result of heave and beating of the waves,characterized in that the hoisting cable (16) is guided over cablepulleys (20) which are connected to the ends of the compensator (21),the mast is designed in the form of a tube or sleeve, and thecompensator (21) is placed in the mast (2).
 3. The hoisting deviceaccording to claim 2, characterized in that the hoisting means areprovided with two winches, (18, 19) each end of the hoisting cable (16)being wound into a separate winch (18, 19).
 4. The hoisting deviceaccording to claim 3, characterized in that the winches (18, 19) aredriven by a plurality of motors with low inertia.
 5. The hoisting device(1) according to claim 2, characterized in that the hoisting cable (16)is also guided over the pulley wherein the pulley further comprises atleast one loose pulley (17) which is movable between a first position,in which the loose pulley (17) is connected to the mast (2), and asecond position, in which the loose pulley is connected to the trolley(10).
 6. The hoisting device (1) according to claim 5, characterized inthat the at least one pulley is fitted relative to the center of themast (2).
 7. The hoisting device according to claim 5, characterized inthat the at least one pulley is accommodated in a housing (53), which atleast on the bottom side is provided with locking elements (104) forfixing the at least one pulley on the trolley (10).
 8. The hoistingdevice according to claim 7, characterized in that the locking elements(104) are equipped with a hydraulic actuation device.
 9. The hoistingdevice according to claim 2, characterized in that the hoisting deviceis provided with a connecting cable (105), for connecting the vessel toa stationary section, such as a top side of a riser (78), whichconnecting cable (105) is guided over the cable pulleys (20) connectedto the end of the compensator (21), in order to be able to exert a forceupon the compensator (21) with the connecting cable.
 10. The hoistingdevice according to claim 9, characterized in that each end of thehoisting cable (16) is wound onto a separate winch (106, 107).
 11. Thehoisting device according to claim 10, characterized in that at leastone of the winches (106, 107) is provided with a slip brake, for payingout the connecting cable (105) when a maximum pulling force in theconnecting cable (105) is exceeded.
 12. The hoisting device according toclaim 9, characterized in that the connecting cable (105) is also guidedover loose pulleys, which are movable between a first position, in whichthe loose pulleys are connected to the mast (2), and a second position,in which the loose pulleys are connected to a stationary section, suchas the top side of the riser (78).
 13. The hoisting device according toclaim 2, characterized in that the mast (2) is provided at the top side,on both sides of the hoisting cable (16), with a fastening (101) forattaching a pull rod or pull cable (102).